A control circuit applied to a display includes a receiving interface, an image processing circuit, and a backlight control circuit. The receiving interface is arranged to receive an image data from an image source, wherein the image data has an unfixed frame rate. The image processing circuit is arranged to receive the image data from the receiving interface and determine a frame rate of the image data. The backlight control circuit is arranged to generate a control signal to a display panel according to the frame rate, to control brightness of a backlight module of the display panel.